1. Field of the Invention
The present invention relates to a counterweight arm mechanism, particularly to a passive counterweight arm mechanism that uses an extension spring to provide tension, and more particularly to a counterweight arm mechanism that can adjust the stretched length of the extension spring to adjust the tension of the tension system. Said tension system refers to a dragline tension system comprising an extension spring and a dragline.
2. Description of Related Art
Counterweight arms are commonly seen mechanical devices with wide applications in, for example, counterweight arm suspenders, medical shadowless lamps, robot arms, counterweight arm lamps etc, wherein, counterweight arm lamps are very common equipment in living and working environments.
A counterweight arm lamp is a lamp with a foldable and extendable lamp arm for diversified lighting needs.
Generally, a counterweight arm lamp has a structure similar to human arm. Apart from the light source and lampshade, it has a front lamp arm, a joint, a support arm, and a base.
The light source and lampshade are configured on the front end of the front lamp arm, the rear end of the lamp arm is connected to the support arm through the joint, and the joint has a rotating shaft structure, so that the front lamp arm can be folded downward or lifted upward in a vertical plane; the other end of the support arm is connected to the base. Between the support arm and the base, usually there is also a rotating shaft structure, so that, in relation to the base, the support arm can be adjusted for an appropriate angle of inclination and can rotate horizontally.
Hereafter, if not otherwise specified, the front lamp arm and the support arm are collectively referred to as the lamp arm. When the lamp arm is tilted or stretched, it will be subject to a torque generated by the force of gravity, and will tend to droop. Therefore, it must rely on the tension of a tension system and the frictional force of the rotating shaft structure or a reverse balance torque to resist the force of gravity, so that the lamp arm can stay at the tilted or stretched position.
When the lamp arm of the counterweight arm lamp is stretched to the horizontal position, the torque on the lamp arm generated by the force of gravity reaches the maximum degree. At this point, the tension system of the lamp arm shall have sufficient tension to resist the torque generated by the force of gravity, so that the stretched lamp arm can stay still and will not droop.
However, the tension of the tension system on the lamp arm of a conventional counterweight arm lamp is directly proportional to the stretched length of the extension spring. When the lamp arm of the counterweight arm lamp is folded downward from the horizontal position, the extension spring will be stretched to a great length, causing a high spring stress. Therefore, the lamp arm of the counterweight arm lamp can not be folded for a large angle, or, due to a large downward folding angle, the extension spring is stretched to its limit, causing fatigue of the extension spring. Similar problems are found in patent literatures like: U.S. Pat. No. 2,076,446, U.S. Pat. No. 2,787,434, U.S. Pat. No. 5,016,153 etc.
To further understand the performance of the conventional counterweight arm in prior-art counterweight arm lamps, below are detailed descriptions with reference to the accompanied drawings.
Firstly, FIG. 1 is a working drawing of the extension spring of a prior-art counterweight arm lamp, which discloses a common counterweight arm mechanism of a counterweight arm lamp. A conventional counterweight arm 1 is a third-class lever with pivot point on the horizontal rotating shaft X of the counterweight arm perpendicular to its movement plane, the load W is located on the conventional counterweight arm 1, on a remote position beyond the rotating shaft X of the counterweight arm, and the point of application D is located between the pivot point and the load.
Due to the tension of the conventional tension system 3 of the conventional counterweight arm 1 and the frictional force of the rotating shaft X of the counterweight arm, the conventional counterweight arm 1 can stay at a stretched position and will not droop.
In FIG. 1, the conventional counterweight arm 1 stays at the horizontal position. When the conventional counterweight arm 1 is folded downward, i.e., to the position marked by the dotted line in FIG. 1, the extension spring S of the conventional tension system 3 is stretched, with the stretched length being ΔL.
In this patent description, said conventional tension system 3 refers to an extension spring S or the combination of an extension spring S and a dragline T. Said extension spring S is often hidden inside a tube-shaped lamp arm structure. Said conventional tension system 3 is very commonly seen in counterweight arm lamps sold in the market.
FIG. 2 is another working drawing of the extension spring of a prior-art counterweight arm lamp. The conventional counterweight arm 1 in this drawing is a first-class ever with pivot point on the horizontal rotating shaft X of the counterweight arm. Having the horizontal rotating shaft X of the counterweight arm as the pivot point, the Joint of application D of the extension spring on the conventional counterweight arm 1 and the load W are respectively located on either side of the pivot point. When the conventional counterweight arm 1 is folded downward, i.e., to the position marked by the dotted line in FIG. 2, the conventional tension system 3 is stretched, and in fact, only the extension spring S can be stretched, with the stretched length being ΔL.
In FIG. 1 and FIG. 2, when the conventional counterweight arm 1 is folded further downward, the extension spring S will be further stretched, but such a stretching is unhelpful. In other words, it is an unhelpful stretching because when the conventional counterweight arm 1 is folded downward and move away from the horizontal position, the torque generated by the force of gravity on the conventional counterweight arm 1 is decrementing, while the extension spring S is stretched, with the consequent increased tension being unhelpful. On the contrary, the conventional counterweight arm 1 has a tendency to be pulled back upward, and as a result, the range of folding the conventional counterweight arm 1 downward is limited; Moreover, the excessive unhelpful stretching of the extension spring S may easily cause fatigue of the extension spring.
As shown in FIG. 1, rotating shaft X of the counterweight arm is a horizontal rotating shaft perpendicular to the movement plane of the conventional counterweight arm 1. one end of the conventional tension system 3 is fixed on a fixed point G via a shaft parallel to the rotating shaft X of the counterweight arm, and the other end of the conventional tension system 3 is fixed on the point of application D on the conventional counterweight arm 1 via a shaft parallel to the rotating shaft X of the counterweight arm. The distance from the axis of the rotating shaft X of the counterweight arm to the fixed point G of the conventional tension system on the torque support 2 is R, and the distance to the point of application D on the counterweight arm is KR, where K is proportionality constant. When the conventional counterweight arm 1 is at the horizontal position, The total length of the conventional tension system 3 including the extension spring S and the dragline T is (√(1+K*2))R. In the following sections of this patent description, R will be defined as the radium of the circumscribed circle of a triangle, but here, the distance from the axis of the rotating shaft X of the counterweight arm to the fixed point G of the conventional tension system on the torque support 2 is set as R for the convenience of reference in the following sections.
As indicated by the dotted line in FIG. 1, when the conventional counterweight arm 1 is folded downward from the horizontal position, the conventional tension system 3 is stretched for ΔL, i.e., the extension spring S in the conventional tension system is stretched for ΔL, because the length of dragline T is not changed. It is to be noted here, that, the positions of the extension spring S and dragline T in the conventional tension system 3 shown in FIG. 1 can be exchanged, and after exchange, the tensions on the two ends of the conventional tension system are the same.
When the conventional counterweight arm 1 is folded downward to a position close to its limit, i.e., the conventional counterweight arm 1 is almost vertically downward, the length of the conventional tension system 3 will be close to (R+KR), (R+KR) being the maximum length to which the conventional tension system 3 can be stretched. Hence, the maximum length increased due to unhelpful stretching of the extension spring S is:ΔL(maximum value)=(R+KR)−(√(1+K*2))R;  Formula 1The technical solution of the present invention is to eliminate or reduce the increased length ΔL due to unhelpful stretching of the extension spring S of a conventional tension system 3. In other words, the object of the present invention is to eliminate or improve the deficiency caused by unhelpful stretching of the extension spring S.